Counterbalance valves are hydraulic valves configured to hold and control negative or gravitational loads. They may be configured to operate, for example, in applications that involve the control of suspended loads, such as mechanical joints, lifting applications, extensible movable bridge, winches, etc.
In some applications, the counterbalance valve, which may also be referred to as an overcenter valve, could be used as a safety device that prevents an actuator for moving if a failure occurs (e.g., a hose burst) or could be used as a load holding valve (e.g., on a boom cylinder of a mobile machinery). The counterbalance valve allows cavitation-free load lowering, preventing the actuator from overrunning when pulled by the load (gravitational load).
As an example, a pilot-operated counterbalance valve could be used on the return side of a hydraulic actuator for lowering a large negative load in a controlled manner. The counterbalance valve generates a preload or back-pressure in the return line that acts against the main drive pressure so as to maintain a positive load, which therefore remains controllable. Particularly, if a speed of a piston of the cylinder increases, pressure on one side of the cylinder (e.g., rod side) may drop and the counterbalance valve may then act to restrict the flow to controllably lower the load.
When a directional control valve is operating in a load-lowering mode, the pilot-operated counterbalance valve is opened by a pressurized pilot line. To protect both directions of motion of a fluid receiving device against a negative load, a counterbalance valve may be assigned to each of the ports of the fluid receiving device. Each counterbalance valve assigned to a particular port may then be controlled open via cross-over by the pressure present at the other port. In other words, a respective pressurized pilot line that, when pressurized, opens a counterbalance valve is connected to a supply line connected to the other port. A counterbalance valve may also be configured as a pressure relief valve in one flow direction and a check valve for free flow in the opposite direction.
A counterbalance valve may have a spring that acts against a movable element (e.g., a spool or a poppet), and the force of the spring determines a pressure setting of the counterbalance valve. The pressure setting is a pressure level that causes the counterbalance valve to open and allow fluid flow therethrough. In examples, the counterbalance valve is configured to have a pressure setting that is higher (e.g., 30% higher) than an expected maximum induced pressure in an actuator controlled by the counterbalance valve.
However, this configuration may render operation of the counterbalance valve energy inefficient. Particularly, the expected maximum induced pressure might not occur in all working conditions, and configuring the counterbalance valve to handle the expected maximum induced pressure may cause a large amount of energy loss.
For instance, an actuator may operate a particular tool that experiences a high load in some cases; however, the actuator may operate another tool that experiences small load in other cases. In the cases where the actuator operates a tool that experiences a small load, having the counterbalance valve with a high pressure setting is inefficient. The hydraulic system provides a high pilot pressure to open the counterbalance valve, and the counterbalance generates a large backpressure thereby causing the system to consume an extra amount of power or energy that could have been avoided if the counterbalance valve has a lower pressure setting.
As another example, an actuator of a mobile machinery may be coupled to the machine at a hinge and as the actuator rotates about the hinge the kinematics of the actuator change, and the load may increase or decrease based on the rotational position of the actuator. In some rotational positions, the load may be large causing a high induced pressure, but in other rotational positions the load may be small causing a low induced pressure.
Configuring the counterbalance valve to handle the large load and high induced pressure renders operation of the hydraulic system inefficient when the load is small. Due to the high pressure setting of the counterbalance valve, a large pilot pressure is provided to open the counterbalance valve and a large backpressure is generated, whereas for the small load a low pilot pressure could have been used. The increased pressure level multiplied by flow through the actuator results in energy loss that could have been avoided if the pressure setting of the counterbalance valve is lowered based on conditions of the hydraulic system.
Therefore, it may be desirable to have a counterbalance valve with a pressure setting that could be varied during operation of the hydraulic system. Such variation could render the hydraulic system more efficient.